Diagnostic challenges of low-grade central osteosarcoma of jaw: a literature review.

UNLABELLED
Low Grade Central Osteosarcoma (LGCO) is a rare subtype of osteosarcoma that is less aggressive than conventional osteosarcoma. The importance of LGCO lies in the fact that regarding microscopic and radiographic features, it occasionally simulates some benign jaw lesions and would consequently be misdiagnosed in many patients. The present study was conducted to collect the information and descriptive analyses related to ten cases reported between 1987 and 2010, including a sample reported by the authors emphasizing on diagnostic errors and the prevailing misdiagnosis. The aforementioned reports were gathered in full-texts through Google and PubMed search engines.


CONCLUSION
The results of this study showed that the pathologists should exactly evaluate the clinical, radiographic, and histopathologic features in order to observe the evidence of invasion.

Introduction phasis on epidemiologic, radiographic, and microscopic aspects as well as diagnostic errors. The abovementioned reports were gathered in full-texts through-Google and PubMed search engines.

Radiographic Features
Like other body bones, [11,[51][52][53] gnathic LGCOsmight be radiographically shown as osteolytic, osteoblastic, or mixed lesions with irregular margins. [53] Some specific radiographic features are ill-defined margins and cortical plate destruction with or without invasion into soft tissues, irregular widening of periodontal ligament space and the sunray appearance; however, these features are not always seen. [28,54] Based on the radiographic findings, in two cases out of all investigated samples, there were misdiagnosis of a giant cell granuloma [31] and a benign fibroosseous lesion. [37] In this study, the radiographic features of 7 cases [24,[32][33][34][36][37][38] were in favor of malignancy on the onset, but occasionally these important features were
In two investigated samples the lesion that had been first diagnosed as a fibrous dysplasia turned to LGCO with focal area of high-grade osteosarcoma in later recurrences with lesion development in adjacent structures.The proliferation of spindle cells with defined atypia and production of osteoid, chondroid, and formation of irregular osteoid trabeculae were observed.

The most important factor for differentiation of
LGCO from fibrous dysplasia is to observe an infiltrative growth pattern. These patterns are described as surrounding pre-existed bone trabeculae with tumor, tumoral cells infiltration into bone marrow, cortex destruction by tumor, and tumor invasion into soft tissues. [37,57] Based on the quality of ossification in LGCO, three different patterns have been reported so far including fibrous dysplasia-like, parosteal osteosarcoma-like, and desmoid-like. [57] Fibrous dysplasia-like type includes irregular spicules of woven bone that sometimes resembles the classic pattern of Chinese script writing. [37,57] However, compared to the branched, delicate, and curvilinear trabeculae in fibrous dysplasia, the coarseness of bone trabeculae in LGCO is a useful guide [13] (Figure   3). LGCO may resemble parosteal osteosarcoma from the microscopic point of view. Both of these lesions have low cellularity, low amount of mitosis and minimum cellular atypia. [25][26] LGCO may show long and parallel strips of lamellar bone that is microscopically non-diagnosable from parosteal osteosarcoma. [57] In this case, radiographic control is very useful to verify the tumor inter-medullary origin. [26,35] Desmoid-like pattern has the least prevalence. Desmoplastic fibroma is a benign bony neoplasm formed from fibroblastic and myofibroblastic proliferation in a heavy collagenous stroma and like LGCO, it can destroy cortex and infil-trate into soft tissues. [57] No osteoid production is observed in desmoplastic fibroma and it lacks mitotic figures. [15,58] Osteoblastoma-like osteosarcoma is a rare variant of osteosarcoma (1.1-1.4%). [26,59]  Therefore, while radiographic features suggest an aggressive lesion, the biopsy should contain peripheral areas of the tumor or the overlying cortical bone. [60] Chondromyxoid fibroma-like osteosarcoma is a completely rare subgroup of low-grade osteosarcoma. [38,55] Similar to its benign counterpart, chondromyxoid-like osteosarcoma includes some loosely aggregations of stellate, spindle, or polygonal cells in a myxoidstroma. Although the most important diagnostic feature is the production of osteoid by tumor cells, this feature has never been observed in chondromyxoid fibroma. [55,61] Solid areas of an aneurismal bone cyst might sometimes be mistaken for LGCO. Aneurismal bone cyst is a benign lesion that hardly ever occurs in craniofacial area. Solid type of this lesion comprises only 5% of all cases and its occurrence in jaws is extremely rare.
Aneurismal bone cyst is more cellular than LGCO and has a prominent mitotic activity. [62] Conclusion For early diagnosis of gnathic LGCO and preclusion of misdiagnosis as a benign lesion, the pathologists should exactly evaluate the clinical and radiographic features in order to observe the peripheral border, cortical bone destruction, and invasion to the soft tissues.
An excisional biopsy, which includes overlying soft tissue, cortical bone, and the medullary portion of the lesion is needed and curettage should not be done.
By thorough evaluation of various sections of specimen, two important features should be taken into account: 1-Osteoid production by tumor cells 2-Any observable infiltrative pattern. Therefore, the general histomorphologic appearance of the lesion might be more helpful than surveying cellular features.

Conflict of Interest
None to declare.